Tubular prostheses or “stents” are often implanted within blood vessels, for example, within the coronary and carotid arteries, for treating atherosclerotic disease that may involve one or more stenoses. Stents generally have a tubular shape capable of assuming a radially contracted condition to facilitate introduction into a patient's vasculature, and an enlarged condition for engaging the vessel wall at a treatment location.
Plastically deformable stents have been suggested that are initially provided in their contracted condition, and placed over a balloon on an angioplasty catheter. At the treatment location, the balloon is inflated to plastically deform the stent until it is expanded to its enlarged condition.
Self-expanding stents have also been suggested that are biased to assume an enlarged condition but may be radially compressed to a contracted condition. The stent may be mounted to a delivery device and constrained in the contracted condition during delivery, for example, by an overlying sheath. At the treatment location, the stent may be released, for example, by retracting the sheath, the stent automatically resuming its enlarged condition to engage the vessel wall.
In addition to tubular stents, coiled-sheet stents have been suggested that include a flat sheet rolled into a spiral or helical shape having overlapping inner and outer longitudinal sections. Such stents generally have a lattice-like structure formed in the sheet and a plurality of fingers or teeth along the inner longitudinal section for engaging openings in the lattice. Once deployed at a treatment location, the fingers may engage openings in the lattice to lock the stent in the enlarged condition.
One of the problems with many stent structures, whether balloon-expandable or self-expanding, is that they substantially expose the underlying wall of the treatment location. For example, helical wire stent structures generally have substantial gaps between adjacent turns of the wire. Multi-cellular stent structures, which may include a series of slotted or zig-zag-shaped cells, create large spaces within and/or between the cells, particularly as they expand to their enlarged condition. The lattice structure of coiled-sheet stents generally also includes relatively large openings.
Thus, despite holding the wall of the treatment location generally open, the openings or gaps in these stents may substantially expose the bloodstream to plaque, tissue prolapse, or other embolic material attached to the wall of the vessel. This embolic material may be inadvertently released during or after deployment of the stent, and then travel downstream where it may cause substantial harm, particularly if it reaches a patient's neurovasculature.
One proposed solution to address the issue of embolic containment is to cover a conventional stent with a fabric or polymer-type material. This solution has met with limited success, however, because of the propensity to form false lumens due to poor apposition of the covering and the vessel wall.
Accordingly, it is believed that a stent capable of supporting the wall of a blood vessel being treated, while substantially minimizing exposure of embolic material to the bloodstream, would be considered useful.